In a large mixing bowl, whip the butter till it’s pale and fluffy.
Add the white sugar and brown sugar and beat 1-2 minutes until smooth.
Add the egg, egg yolk, and vanilla extract and mix thoroughly.
In a medium bowl, combine the dry ingredients: flour, chocolate shavings, baking powder, and salt.
(If using an electric stand mixer, switch to the paddle attachment) Gradually stir the dry ingredients into the cream mixture on the lowest mixer speed until combined.
Divide the dough into two parts and wrap each in plastic wrap. Refrigerate for 2 hours.
Preheat the oven to 375°F.
Sprinkle powdered sugar onto the countertop or a silicone mat and roll out the dough to ¼ inch thick.
Use a cookie cutter to cut out shapes, and place them onto cookie trays lined with a silicone baking mat or parchment paper, leaving an inch between cookies.
Bake the cookies until the edges just begin to show a light golden color, about 10-12 minutes. Allow the cookies to remain on the baking sheet for 4 more minutes, then move the cookies to a wire baking rack and allow them to cool completely before adding the icing.
Mocha Icing (option 1)
In a mixing bowl, add the powdered sugar, meringue powder, and 5 tablespoons water. Whip on high for 7-10 minutes.
Remove ¼ cup of white icing and put into a pastry bag with a small round tip (Wilton #4)
Add the cocoa powder, espresso powder, and 3 more Tablespoons water to the mixing bowl and mix thoroughly. The icing should be slightly runny and good for piping.
Using a pastry bag with a medium round tip (Wilton #7), pipe the icing around the edge of the cookie and continue spiraling towards the center. The icing swirl will run together and form a smooth layer of icing.
While the icing is still wet, pipe latte art in the center of the cookie.
Leave the iced cookies uncovered for several hours to dry completely before stacking them or transferring them to an air-tight container.
Hot Cocoa Icing (option 2)
In a mixing bowl, add the powdered sugar, meringue powder, hot cocoa mix, and water. Whip on high for 7-10 minutes. The icing should be slightly runny. If not, add 1 teaspoon of water at a time and continue to whip until it’s a good consistency for piping
Using a pastry bag with a small round tip (Wilton #7), pipe the icing around the edge of the cookie and continue spiraling towards the center. The icing swirl will run together and form a smooth layer of icing.
Sprinkle the marshmallow bits on top of the cookie while the icing is still wet. Be sure to eat any leftovers.
Leave the iced cookies uncovered for several hours to dry completely before stacking them or transferring them to an air-tight container.